It is conventional to provide a digital VTR which encodes image data, and records and plays back the encoded image data on and from a magnetic tape. In recent years, a device which encodes image data by an inter-frame coding method such as MPEG or the like, and records and plays back the encoded image data on and from a magnetic tape is also known.
Since MPEG encodes the difference between frames of image data, decoding cannot be done by only this difference data, and image data of a reference frame is required to decode encoded data. Also, since frames have all different data sizes in MPEG-encoded image data, the recording positions of frame data on a magnetic tape are not constant. For this reason, when image data which is MPEG-encoded and recorded undergoes high speed playback, since a magnetic head cannot accurately scan tracks on the tape, all data recorded on the tape cannot be played back, but data are discretely played back.
For this reason, the inter-frame encoded difference data and reference frame data are unlikely to be obtained together, and image data of frames encoded by intra-frame coding alone can be decoded. Hence, it becomes difficult to obtain a high-quality playback image.
To solve this problem, a technique for generating image data for high speed playback using only intra-frame encoded image data in addition to normal encoded image data, and recording the image data for high speed playback at positions scanned by the head on respective tracks upon high speed playback has been proposed (see Japanese Patent Laid-Open No. 9-214889, counterpart U.S. Pat. No. 6,292,621). With this technique, a high-quality playback image can also be obtained upon high speed playback.
Also, the following technique has been proposed (see Japanese Patent Laid-Open No. 2004-242172, counterpart US2004156619). A moving image data sequence including moving image data for normal playback which is encoded according to an MPEG2 packetized elementary stream (PES) format and image data for high speed playback is recorded to form a large number of tracks. When the moving image data for normal playback and image data for high speed playback are played back to be output as digital data, the moving image data for normal playback in the PES format and the image data for high speed playback, which are played back, are multiplexed in an MPEG2 transport stream (TS) format and the multiplexed data is output to a digital interface (DIF).
One example of the prior art, which corresponds to Japanese Patent Laid-Open No. 2004-242172, relates to the multiplexing of the image data for high speed playback in an encoded state, and the outputting of the image data to the DIF. Therefore, an external apparatus as an output destination need not generate new image data for high speed playback.
Processing in the external apparatus occurs as follows. Upon reception of moving image data for normal playback and image data for high speed playback, which are output from a playback apparatus, the moving image data can be decoded and displayed on a display unit of the apparatus, so as to visually confirm the received contents. In this case, when the transfer rate of the moving image data for normal playback is high, and the processing capability and displaying capability of the external apparatus are low, decoding processing and display processing cannot be done in time upon decoding and displaying the moving image data for normal playback on the display unit, thus generating a disturbance such as block noise or the like on the display screen.
The present invention has been made to solve such problems, and has as its object to allow playback for confirming the received contents even when the transfer rate of moving image data for normal playback is high and the processing capability and displaying capability of an external apparatus on the receiving side are low.